PORTLAND (AP) — Loren Parks, the biggest political campaign contributor in Oregon history, has challenged an Internal Revenue Service allegation that he owes more than $75,000 in federal taxes.

The IRS says one of his tax-exempt foundations spent $639,000 on Oregon radio commercials from 1997 to 2000, and that money should have been taxed because the advertising sought to influence public opinion on ballot measures.

In 1997, for example, the IRS alleges that about $65,000 in spending went for radio ads supporting Measure 49, which amended the Oregon Constitution to restrict inmate lawsuits and allow interstate shipment of prison-made products. The IRS, also is seeking to collect taxes on the foundation’s spending for radio ads that were aired from 1998 to 2000 and related to ballot measures on mandatory minimum sentencing, review of state administrative rules, victims’ rights, and limiting state spending.

Under federal law, tax-exempt status is intended for foundations with nonpolitical causes.

A trial is scheduled to begin Nov. 17 in Nevada, where Parks moved several years ago.

A Portland attorney representing Parks said his client can afford to pay the IRS but thinks the agency’s position is an infringement of free speech.

“He believes the ads were approved and allowed under the rules,” Kevin O’Connell said. “As a matter of principle, he wants to see that through.”

IRS officials declined to comment on the case.

Parks, 82, the owner of an Aloha-based medical equipment company, has given $12 million to Oregon initiative and candidate campaigns in the past 15 years. That includes $3 million spent for this year’s election, placing six measures on the Nov. 4 ballot.